Sealed-off ignitron



Dec. 13 1938. D. E. MARSHALL Q saegiiu SEALED-OFF IGNITRON Filed Feb. 11, 1938 INVENTOR Donald B. Marshall.

ATTORNEY WITNESSES: lmim'olwb L. 7W 601/40 Patented Dec. 13, 1938 UNITED STATES PATET OFFIQIE SEALED-OFF IGNITRON tion of Pennsylvania Application February 11, 1938, Serial No. 189,970

11 Claims.

My invention relates to sealed-off ignitrons and more particularly to improvements in the exciting electrode of the type mounted with the anode portions in concentric relation.

In the construction of electric current rectifiers of the metallic vapor arcing type, where starting electrodes are brought in through the side walls of the metal tank making up the rectifier, or through the cover plate, or similar designs with the starter brought in otherwise, difficulties have been experienced in the manufacture of such designs due principally to the assembly of the rectifier. According to these designs, several seals need to be provided for sealing the anode and the starting electrode which are inserted into a gastight metal tank. Likewise, several means are provided to properly support the electrodes from the tank wall.

According to my invention, the rod of the starting electrode is brought down through the anode including the stem and cap portions in a concentric relation. The insulators and supporting members are designed to withstand the electrical, thermal and mechanical stresses to which they are exposed. The anode is supported from a cap preferably made of an alloy steel composed of iron, nickel and cobalt which acts as an electrical connection as well as part of a seal for the insulation of the anode from the cathode and the anode to the starter electrode terminal.

The anode stem is of special construction to allow small heatfiow to the anode cap,thus making it possible to keep the upper seals cool by a radiator when the anode is subjected to working temperatures in the neighborhood of 600 C. The glass seal for the starter rod is so designed that any condensation of mercury in the upper seal will be returned down the outside of the anode shield and then to the cathode instead of through the openings in the anode portions provided for the starter rod which has been considered a backfire hazard. One steam weld is used to keep the number of welded joints in the device to a mini mum, thus avoiding trouble due to leaky welds.

The alloy steel used for supporting the anode and which is in contact with the glass seal, has approximately the same coeflicient of expansion as the glass forming the seal and is easily wet by the glass when hot.

It is therefore an object of my invention to provide a seal for an electric power rectifier in which the metal portions sealed to the glass portions have substantially the same coefiicient of expansion.

It is another object of my invention to construct an electric power rectifier in which the exciting electrode is extended through the anode member in concentric relation therewith.

Still further, it is an object of my invention to provide a sealed vapor discharge device of such design that any mercury condensing in the upper portions of the device will be prevented from falling through the anode assembly, thus elimihating backfire hazards.

It is another object of my invention to construct a sealed-off metal discharge device which is simple and inexpensive to manufacture, and which makes possible considerable simplification of the anode cap construction.

Other objects and advantages of my invention will be apparent from the following detailed description taken in conjunction with the accompanying drawing in which:

Figure 1 is a sectional elevation of a metal-glass sealed-off rectifier showing the anode and exciting electrode construction according to my invention, and

Figs. 2, 3 and 4 are detail views of anode assembly members according to my invention.

Referring more particularly to the drawing by characters of reference, I show an electric discharge device 3 comprising an evacuated envelope which is essentially made up of a lower metal portion 5, an upper metal portion 9 and a glass portion I! preferably boro-silicate glass therebetween.

The lower metal portion 5 consists of a metal cup I having a quantity of mercury therein forming the cathode i3 of the device 3 and which is provided with a flanged portion [5. A cover plate I l for the cathode cup 7 has a flanged portion I9 spun from one piece of Kovar which is an iron base alloy having a nickel and cobalt content such as disclosed and claimed in United States Patent No. 1,942,260 granted January 2, 1934, on application of Howard Scott, and assigned to the same assignee as the present invention.

The cover plate I! forms part of the insulating seal between the anode 2| and the cathode IS. The neck portion 23 of the cover plate I! is machined, inside and out, for the glass seal and a thickness of no less than three sixty-fourth inch at the flanged portion IQ of the cover plate I! should be maintained, as this is the minimum thickness to which good welds can be made. The flanged portions l5 of the cathode cup I and cover plate I! are seam welded together by a process which will be fully explained later.

The upper metal portion 9 of the device 3 is in the form of an anode cap which is made of the same material as the cathode cover plate IT. The cap 9 has a flanged portion which is provided with a plurality of holes 21 for fastening a radia tor 29 above it. The lower portion of the cap 9 has a downwardly projecting threaded metal member 3| from which is suspended a graphite anode 2| through a metal stem 33. Sealed to the upper side of the anode cap 9 is a reentrant glass stem 35 which holds the starter rod 31. By providing openings in the anode cap 9, the anode stem 33 and the anode head 2|, the starter rod 31 may be extended down through the anode members 23, 33 and 2| in a concentric relation. However, the openings thus provided require a glass umbrella 39 above the opening in the anode cap 3 through which the starter rod 31 passes and a plurality of openings 4| in the anode cap 9 are provided to act as drain holes for the return of mercury which condenses in areas above the anode cap 9. The passageway of the mercury thus condensed is such that it prevents the condensed mercury from falling through the anode assembly, a condition considered a backfire hazard.

The glass portion ll of the device 3 is sealed to the anode cap 3 at one end and to the cathode cover plate H at the other end. The sealing of the glass H to these parts i? and 9 is still in the status of an art rather than a science. Nevertheless, the glass blower learns from experience how to obtain the proper oxide on metal surfaces I? and 9. It was discovered that too much oxide results in a leaky seal while too little forms a weak seal. However, if the glass I! is properly worked, a smaller amount of oxide produces the best results. In sealing the glass portion H to the metal portions H and 9, a cup of glass is made to flt around the outside of the metal portions H and S and sealed thereto. The center of the cup is then opened and the glass folded over the edge and sealed. The glass portion H is next sealed to the glass on the metal portions i! and 9 which has been scaled to it beforehand as above described.

The anode cap 9 which acts as an electrical connection as well as an anode support forms part of the seal for insulating the anode 2| from the cathode l3 and a starter rod terminal 31. The stem 33 connecting the anode 2| to the cap 9 is of special construction to allow small heat flow to the anode cap 9, thus making it possible to keep the upper seals cool by a radiator 29 when the anode 2| operates at working temperatures in the neighborhood of 600 C.

A cylindrical shield 42 preferably of sheet metal is mounted over the anode stem 33 and covers a substantial portion of the lateral surfaces of the anode head 2|.

An insulator 43 separates the anode shield 42 from the anode stem 33 to decrease the probability of mercury short-circuiting between the anode 2| and the cathode portion 5. All spacings between the anode 2| and the cover plate I! and between the anode 2| and cathode cup 1 are made as close as judgment will permit to make the glow voltage as high as possible.

Referring to Figure 2, I show a detail view of the anode stem 33 which is suspended by the upper portion from the anode cap 9 of which Figure 3 is a top view. The anode cap 9 has a flanged portion 25 with a plurality of holes 2! for mounting a radiator 29 above it and an additional number of smaller holes 4| located outside the projecting threaded member 3|. In Fig. 4, I show a partial view of the anode cap 9 to indicate the respective locations of the drain holes 4| and the downwardly projecting portion 35 of the anode cap.

In the assembly of the device 3, all glass blowing is first completed, followed by a removal of the oxide from all metal surfaces. The anode shield 42 and the insulator 43 are placed on the anode stem 33 and fastened with nickel wire. The upper part of the insulator 43 is grooved and the lower part of the neck of the shield 42 is expanded. If desired, a wire 46 is wound around the insulator 43 under the expanded portion of the shield 42 to insure that the shield 42 is not too loose as to be in danger of touching the anode 2|. A wire 46 is wrapped in a groove 45 provided in the upper part of the insulator 43 to hold the shield 42 in place in case the device 3 should be held upside down.

One end of the anode stem 33 is screwed into the cap 9 while the anode head 2| is screwed into the other end of the anode stem 33. The starter rod 31 which is secured to the glass stem 35 above the anode cap 23 is extended down through the anode portions 9, 33 and 2| and a high resistance material 47 is fastened onto the threaded end. The rod 3'! is threaded longer than the screw hole in the high resistance material 41 to permit adjustment of the length of the rod 3'! after all glass blowing is completed.

The flanged portion l5 of the cathode cup I and the flanged portion I9 of the cathode plate ii is next seam welded by first spot welding in several places to hold the flanged portions l5 and IS in place while seam welding is done. I have found that the welded flanges should be about three-quarter inch wide or metal tends to blow out from between the two flanges l5 and I9 causing imperfect welds. The flanged portions l5 and IQ of the cathode cup 1 and the cover plate ll must be smoothed to a close fit by either grinding or machining. It appears that the best seam welding is obtained when the two flanges i5 and i9 have approx mately the same thickness.

The device 3 thus assembled without the radiator 29 and water jackets 49 is next out-gassed by baking at 400 C. to remove all gases from the inside walls and other portions of the device 3 which run relatively cold under normal operation. Mercury is next distilled into the cathode cup I by using a still to which mercury can be supplied by a barometric column. The mercury is poured in until the level of the mercury in the cathode cup "I touches the tip of the resistance material 41 as indicated by a test lamp circuit. About 50 c. c. of mercury should be further added above the level just obtained. The anode 2| and other portions which run hotter than 400 C. are outgassed by running the device 3 at reduced voltages on a resistance load. While the baking out process is performed, the device 3 is connected to a vacuum system by a glass stem 35 and allowed to run long enough to reduce the pressure to several microns, at which point the device 3 is sealed-off.

With the 400 C. baking completed, the copper coil 5| which is wound in the form of a double helix is slipped on over the cathode cup 1 and covers the bottom as well as the sides of the cathode cup I. In the assembly, the water inlet 53 and outlet 55 of the copper coil 5| are both at the top thus allowing the cathode cup 1 to be free of any projections such as ignitor connectors. By such an assemblage of the copper coil 5|, the bottom as well as the sides of the cathode cup 1 can'be efficiently cooled. The water jacket 49 is fitted over the copper coils 5| and clamped to the flanged portion I5 of the cathode cup I. It may be desirable to fill the space between the copper coil 51 and the cathode cup I with molten solder 52 to insure a good thermal contact between them.

An aluminum radiator 29 is bolted to the flange portion 25 of the anode cap 9 which is provided with a plurality of holes 21 for this purpose.

It is to be understood that I do not wish to limit my invention to the aforesaid design, for many modifications are possible. For instance, the area above the anode cap 9 where mercury is continually condensed can be filled with porcelain or some similar material thus eliminating the glass blowing operation at this point. Such a seal makes a simpler anode cap construction and removes not only the condensing area, but the holes 4| in the anode cap 9 and the glass umbrella 39 as well. Other parts of the device 3 are capable of being simplified from the standpoint of construction and assembly which will reduce the cost and improve the performance of the rectifier. 1

While I have shown and described certain specific embodiments of my invention, it will be understood that many changes and modifications can be made therein without departing from the true spirit of my invention and the scope of the appended claims.

I claim as my invention:

1. In an electric discharge device comprising an evacuated container partly of a metal wall and partly of a glass wall, a vaporizable material in said container, said metal wall having several sections sealed to opposite ends of said glass wall, one of said metal sections comprising a cathode cup and another of said metal sections comprising a cap for an anode member within said container, said anode member including a headportion and a stem portion in engageable relation with said anode cap, an insulating member sealed to another end of said metal cap, a make-alive stem secured to said insulating member and extending through apertures in said anode portion, a tip of resistance material secured to the extended end of said make-alive stem and partially in contact with the vaporizable material.

2. In an electric discharge device comprising an evacuated container consisting partly of a metal wall and partly of a glass wall, said metal wall having several sections sealed to opposite ends of said glass wall, a portion of one of said metal sections comprising a cathode cup while the remaining portion forms a closure plate for said cathode cup, another of said metal sections comprising a cap for an anode member within said container, said anode member including a head portion and a stem portion for connecting said head portion to said anode cap, a make-alive stem extending through said anode portions, a tip of resistance material attached to one end of said make-alive stem, and means for supporting said make-alive stem at the opposite end thereof, said supporting means serving as part of a vacuumtight seal connection for said discharge device.

3. In an electric discharge device comprising an evacuated container consisting partly of a metal wall and partly of a glass wall, said metal wall having several sections sealed together by said glass wall, said sections sealed to said glass wall being composed of a material having substantially the same coefiicient of expansion as said glass wall, an anode member within said container, said anode including a head portion suspended from one section of said metal wall by a stem portion, an insulating material sealed to the other end of said metal wall supporting said anode head, an electrode stern extending through the center of said anode portions and attached to said insulating material, a tip of resistance material secured to the extended portion of said electrode stem, said tip being in permanent contact with a vaporizable material contained in a cathode cup forming a portion of another section of said metal wall.

4. In an electric discharge device comprising an evacuated container, an anode having an enlarged head portion, a stem portion and a cap portion, a cathode member constituting a lower portion of said container, a cover plate forming another portion of said container and in tightfitting engagement with said cathode member, a tubular glass wall sealed to and separating said cathode cover plate from said anode cap, said cover plate and said anode cap being composed of a material having substantially the same coefficientof expansion as said glass wall, an insulating material in vacuum-tight relation with another end of said anode cap, a make-alive stem having a tip of resistance material supported from said insulating material and extending through said anode portions in concentric relation therewith.

5. In an electric discharge device comprising an evacuated container, an anode having an enlarged head portion, a stem portion and a cap portion, a cathode member constituting a portion of said container, a cover plate forming another portion of said container and being in tight fitting engagement with said cathode member, a tubular glass wall in sealed relation with and separating said cover plate from said anode cap, said cover plate and said anode cap composed of a material having substantially the same coefiicient of expansion as said glass Wall, apertures centrally located in said anode portions, a starting electrode extending through said apertures, means for supporting said starting electrode, said supporting means constituting a part of a seal for said discharge device, and a plurality of openings in said anode cap affording a passage way for the return flow of vaporizable material condensed above said anode cap.

6. The combination with an electric current rectifying structure of the metallic vapor type having a casing forming an evacuated chamber, said casing including a glass member and a plurality of metal members, at least two of said metal members welded in vacuum-tight relation, one of said welded members forming a cathode cup for said device, another of said welded members forming the cover plate for said cathode cup, said glass member sealed to and separating said cover plate member and a third metal member, an anode including a head portion and a stem portion in said container, a starting electrode extending through said third metal portion and said anode members, a supporting structure for said starting electrode, said supporting structure serving in addition as a sealing member for said device.

7. The combination with an electric currrent rectifying structure of the metallic vapor type having a casing forming an evacuated chamber, said casing consisting of a plurality of metal sections and a glass section, a hollow anode having a head portion and an engageable stem portion, an anode cap constituting one of said metal sections having a lower portion sealed to one end of said glass section, a cathode cup provided with a cover plate constituting the remaining portions of said metal sections, said cathode cover plate sealed to another end of said glass section,

a shield fitted over said anode stem and substantially surrounding the lateral surface of said anode head, an insulator between said shield and said anode stem, a make-alive electrode extending through openings centrally located in said anode cap and said anode portions, a supporting structure for said make-alive electrode, said supporting structure forming part of a glass seal in vacuum-tight engagement with the upper portion of said anode cap.

8. The combination with an electric current rectifying structure of the metallic vapor type having a casing forming an evacuated chamber, said casing including a glass section and a plurality of metal sections, one of said metal sections comprising a cathode cup, a metallic liquid in a portion of said cathode cup, another of said metal sections comprising a cover plate for said cathode cup, a third metal section forming a supporting structure for an anode member therein, said glass section sealed to and separating said second metal section from said third metal section, said anode member including a head portion connected to said metal supporting structure by a metal stem, a shield mounted over said metal stem and substantially surrounding the lateral surfaces of said anode head, an insulator between said anode stem and said shield, a starting electrode extending through and in concentric relation with said anode structure, means insulated from said anode supporting structure for supporting said starting electrode, openings in said anode supporting structure affording a passageway for the return flow of vaporized metallic liquid condensed above said anode supporting structure, said openings so located that the condensed metallic liquid passes over said anode shield.

9. In an electric discharge device comprising a l container consisting of a metal section and a glass section, a hollow anode having a head portion and a cap portion, said head portion including an upwardly projecting threaded male member, said cap portion including a downwardly projecting male member, a metallic hollow stem having a threaded female member at each end thereof, said head portion and said cap portion secured to said stem at opposite ends thereof, a closure plate forming part of said metal section sealed to one end of said glass section while said anode cap portion is sealed to the opposite end of said glass section, another part of said metal section forming a cathode cup containing vaporizable material in a portion thereof and in tight fitting engagement with said closure plate, a shield mounted over said hollow stern and substantially surrounding the lateral surfaces of said anode head, an insulator between said shield and said metallic stem, a reentrant non-conducting stem sealed to another end of said anode cap portion, a make-alive rod secured to a portion of said reentrant stern, said make-alive rod extending centrally through said anode portions, a tip of resistance material mounted to the extended portion of said make-alive rod and partially in contact With said vaporizable material in said cathode cup and openings in said anode cap for the return flow of vaporizable material condensed above said anode cap.

10. In an anode construction for an electric discharge device comprising a combination metal and glass container, an anode structure consisting of a head portion, a stem portion and a cap portion, said cap portion including an interior and exterior support, said anode head portion suspended from said interior support of said cap by said stem portion, radiating means mounted on said exterior support of said cap, said radiating means serving to conduct heat transferred to said cap portion from said head portion and a starting electrode extending centrally through said anode portions, said electrode supported by a glass stem sealed to an upper portion of said anode cap.

11. In an electric discharge device comprising an evacuated container consisting of a glass section and a plmality of metal sections, at least two of said metal sections composed of an iron base alloy having a nickel and cobalt content sealed to opposite ends of said glass section, said metal sections sealed to said glass section having substantially similar coefficients of expansion, an anode structure supported from one of said metal sections sealed to said glass section and partially suspended in a third of said metal sections, a starting electrode extending centrally through said anode structure and a supporting structure of non-conducting material for said starting electrode, said electrode supporting structure being sealed to another end of said metal section supporting said anode structure.

DONALD E. MARSHALL. 

